Implement Multisensor firmware and update FSU for robustness

This implements working code for analog voltage acquisition using the multisensor board and pulse counting.  A new tool exists to use this functionality: multisensor.  Multisensor can configure parameters related to analog voltage acquisition and read the pulse counter.  Demo:
```shell
> multisensor  read -c
```
Will continuously read and dump voltages
```shell
> multisensor pulse -c
```
Will continuously read and dump pulse counts.

__NB__ you need to update your FSU with the latest firmware to use the new modtool features for FSU robustness.

Added commands fsu heartbeat and fsu reset to modtool.  Heartbeat makes sure the FSU is there and responding, reset resets the FSU.  

_Also added modtool reset to reset the controller_
__You need to update the controller firmware to the latest version__

Fixes a bug where the controller upon reflashing does not properly reset the bus.